Field of the Invention
The present disclosure relates to a cylindrical extruding die for extruding a seamless tube and to a method for producing a seamless tube.
Description of the Related Art
Electronic apparatuses, such as printers and multifunctional peripherals, use many conductive or semiconductive tube-shaped seamless members (hereinafter referred to as “seamless tube”) for development, transfer, fixing, and other processes. For example, a seamless tube used as an intermediate transfer belt requires flexibility and electrical conductivity. Such seamless tubes are made of a resin composition containing a thermoplastic resin serving as a binder resin and an electronically conductive filler, such as carbon black, dispersed in the thermoplastic resin.
An example of a method for producing a seamless tube with such a resin composition includes the processes of:
(1) putting pellets made of thermoplastic resin containing an electronically conductive filler into an extruder to melt the pellets;
(2) extruding the plasticized resin composition out from a cylindrical extruding die mounted to an end of the extruder to form the plasticized resin composition into a tube; and
(3) cool-solidifying the tube-shaped plasticized resin composition, with the tube shape kept, to produce a seamless tube.
Conductive seamless tubes for use in electrophotographic image forming apparatuses require uniform electrical resistance in a circumferential direction.
Japanese Patent Laid-Open No. 11-170340 discloses a method for molding a seamless tube having uniform circumferential resistance distribution through the process of extruding a thermoplastic resin composition containing a conductive filler, such as carbon particles, into a tube shape. Specifically, the method involves measuring a volume electrical resistance or a surface electrical resistance on the circumference of the cool-solidified extruded tube perpendicular to a direction in which the extruded tube is withdrawn and adjusting the temperatures of at least two portions on the circumference of the extruded molten tube on the basis of the measurements using temperature control units disposed to partially control the temperatures.